1. Field of the Invention
This invention relates to the field of automated grading or analysis of an object, and to the fields of robotics and image processing applied to the grading of an object. More particularly, the invention relates to an automated object grading system in which the objects are coins.
2. Description of Related Art
The value of a collectible coin depends upon its grade, which is an indication of the condition or state of wear of the coin. As with other "expert" appraisal process, coin grading depends to a large extent on the appraiser's skill and experience, and is affected by such randomly variable environmental factors as the type and amount of lighting applied to the surface of the coin being graded. Therefore, conventional manual coin grading techniques are inherently time consuming and suffer from a lack of consistency inherent in all complex manual processes.
Attempts have previously been made to increase both efficiency and consistency in the field of coin grading through the use of automation. In many other fields, it has been possible to completely automate formerly manual processes, resulting in substantial increases in efficiency. Nevertheless, because of the complexity of the coin process, previous attempts to automatically grade coins have not been successful. In general, such systems have achieved only crude approximations of present coin grading standards, for example, by basing a grade on the sum of detracting mark surface areas on a coin. No system has so far been proposed which would fully but consistently duplicate the extremely complex analysis process of the human expert coin grader in such a manner that present coin grading standards, and coins previously graded under the present standards, would be unaffected by changes in the manner in which the coins are graded.
Because the market value of a rare or antique coin may be sharply effected by even very small or subtle differences in grade, it is essential that the grades given a particular coin be both accurate and repeatable. Any new automated method of coin grading must be able to duplicate the results obtained by human coin graders if present standards are to be maintained. However, in view of the present difficulty in achieving consistent manual grading even under the most carefully controlled circumstances, exactly duplicating the results of a human grader one hundred percent of the time would be impossible. Therefore, automation also involves the problem of defining an acceptable degree of correlation between automated and manual grading results by which a new coin grading system could be judged.
A useful measure of the correlation needed to maintain present standards is that the correlation between grades given by an automated system and by a human expert should be the same as the correlation between two different human expert graders. An automated coin grading system would be considered to be acceptable if, for example, two different experts agreed upon a grade 93% of the time and the automated system agreed with each expert at least 93% of the time.
Coin grading involves a very large number of factors, not all of which are easily quantifiable. The grade of the coin depends upon such different factors as strike, luster, mirror, and cameo, as well as the number and nature of flaws on the surface of the coin. In general, no two different types of coins will be graded in exactly the same manner. A particular flaw on one coin, for example, might not be perceived in the same way on another coin depending on the other coin's luster, mirror, and so forth. Analysis of the manner in which the above factors are determined by human graders reveals that coin grading involves literally hundreds or thousands of different considerations, many of which the grader is not even consciously aware of.
An example of an existing automated coin grading system is described in U.S. Pat. No. 4,899,392 to Merton. However, the system of Merton does not attempt to duplicate the actual mental processes of a human expert numismatist, but rather attempts simply to provide a consistent coin grading system intended to replace the present coin grading system without attempting to take into account lighting, luster bands, and other factors which affect the expert grader's reaction to the qualities of a coin and its detracting marks.
In the system of Merton, each detracting mark is assigned a quantity proportional tot he detracting significance of the mark based upon its location and measured surface area, and those quantities are summed to arrive at an amount representative of all of the detracting marks on the selected coin side, after which the sum is correlated with a grde. The system does not account for the different visibility of marks on lighting conditions, the luster of the coins, or the nature of the flaws, but rather simply uses a gross measure of total surface area weighted according to location on the coin.
An expert grader, on the other hand, would tend to grade marks having identical locations and surface areas differently depending on whether the mark was, for example, a scratch, or a lighter, more evenly shaped mark. In addition, the expert would physically manipulate the coin to clearly identify all marks by varying the lighting angle, and the significance of the marks would be judged based on the quality of the background as well as the type, visibility, and location of the marks.
As noted earlier, in order to achieve a truly useful automated coin grading system, and hundreds and possibly thousands of considerations and throughout process which go into determining a final coin grade must therefore be identified. Furthermore, the numerous considerations which go into grading a coin need to be varied for each different type of coin. In order to provide a practical system, a method must be developed for providing a unique set of coin grading criteria for each different type of coin, preferably without starting at "square one" each time.
Provision of an automated coin grading system which overcomes these obstacles, i.e., which takes into accound the numerous considerations and thought processes employed by a human grader in grading a coin, and yet which provides a practical way of varying the resulting grading scripts to accommodate different coin types, has heretofore not been developed.